Alternative transportation fuels have been represented as enablers to reduce toxic emissions in comparison to those generated by conventional fuels. At the same time, tighter emission standards and significant innovation in catalyst formulations and engine controls has led to dramatic improvements in the low emission performance and robustness of gasoline and diesel engine systems.
One approach to addressing the issue of emissions is the employment of fuel cells, particularly solid oxide fuel cells (xe2x80x9cSOFCxe2x80x9d), in a transportation vehicle. A fuel cell is an energy conversion device that converts chemical energy into electrical energy. The fuel cell generates electricity and heat by electrochemically combining a gaseous fuel, such as hydrogen, carbon monoxide, or a hydrocarbon, and an oxidant, such as air or oxygen, across an ion-conducting electrolyte. The fuel cell generally consists of two electrodes positioned on opposite sides of an electrolyte. The oxidant passes over the oxygen electrode (cathode) while the fuel passes over the fuel electrode (anode), generating electricity, water, and heat.
A SOFC is constructed entirely of solid-state materials, utilizing an oxygen ion conductive oxide ceramic as the electrolyte. The electrochemical cell in a SOFC comprises an anode and a cathode with an electrolyte disposed therebetween.
Application and research efforts during the 20th century, into using SOFCs, were generally concentrated in the stationary power generation industry. Because of those SOFC designs, the SOFC was not readily adaptable for use in a transportation vehicle. A transportation vehicle application imposes specific temperature, volume, and mass requirements, as well as real world factors, such as fuel infrastructure, government regulations, and cost. Several other types of fuel cell systems (i.e., proton exchange membrane (PEM) fuel cells) have been adapted for use in transportation vehicles, but require on-board storage or generation of hydrogen, which require complex water management systems for on-board fuel reforming and system hydration. The on-board storage and water management systems add cost and complexity to the overall system.
The drawbacks and disadvantages of the prior art are overcome by an integrated solid oxide fuel cell mechanization.
A method of starting a solid oxide fuel cell system is disclosed. The method comprises pressurizing a main plenum to a first pressure. The main plenum comprises a first supply of fuel, blowers and air control valves. The first supply of fuel and a first supply of air are directed to a preheated micro-reformer. A heated pre-reformate is created in the micro-reformer and discharged from the micro-reformer to a main reformer. The main reformer is preheated with the heated pre-reformate. A second supply of fuel and a second supply of air are introduced to the main reformer. A heated main reformate is created in the main reformer and directed to a waste energy recovery assembly. A cathode supply is heated in the waste energy recovery system and then directed to a solid oxide fuel cell stack in order to heat the solid oxide fuel cell stack.
A method of transitioning a solid oxide fuel cell system to normal operating conditions is disclosed. The method comprises operating a main reformer to produce a reformate from a hydrocarbon fuel and directing the reformate in a first stream and second stream to a waste energy recovery assembly. The first stream is catalytically combusted in the waste energy recovery assembly, producing thermal energy to heat the second stream of the reformate and a cathode supply of air. The second stream of the reformate and the supply of air are directed to a solid oxide fuel cell stack. The solid oxide fuel cell stack is heated to a temperature of about 600xc2x0 C. or greater.
A method of operating a solid oxide fuel cell system is disclosed. The method comprises directing a supply of reformate from a waste energy recovery assembly to a solid oxide fuel cell stack. The solid oxide fuel cell stack uses the supply of reformate and a supply of air to produce electrical energy. The electrical energy is harnessed, a condition of the reformate is sensed, and the supply of reformate and the supply of air are adjusted to meet a demand by a vehicle for the electrical energy.
A method of shutting down a solid oxide fuel cell system is disclosed. The method comprises maintaining a supply of air to the solid oxide fuel cell stack and at least one thermal enclosure. The supply of reformate to the solid oxide fuel cell stack is decreased. The supply of reformate is stopped after an anode oxidation period has passed. The supply of air to the solid oxide fuel cell stack is stopped.
A method of operating a solid oxide fuel cell system is disclosed. The method comprises directing a supply of reformate and a supply of air to a solid oxide fuel cell stack and operating the solid oxide fuel cell stack. The supply of reformate and the supply of air to the solid oxide fuel cell stack is reduced. The solid oxide fuel cell stack is maintained at a standby temperature of about 400xc2x0 C. to about 600xc2x0 C.
A solid oxide fuel cell mechanization for a transportation vehicle is disclosed. The mechanization comprises a solid oxide fuel cell stack in fluid communication with a reformer system, such that the reformer system comprises a main reformer and a micro-reformer. A waste energy recovery assembly is disposed in fluid communication with both the solid oxide fuel cell stack and the reformer system. A system enclosure is disposed around the solid oxide fuel cell stack, the waste energy recovery assembly, and the reformer system. A thermal management system is disposed within the system enclosure. The thermal management system comprises a main plenum and an insulation plenum enclosing a chamber. The chamber comprises the solid oxide fuel cell stack, the reformer system, and the waste energy recovery system. A process air supply is disposed in fluid communication with the thermal management system.
The above described and other features are exemplified by the following figures and detailed description.